1. Field of the Invention
This invention relates to a stainless steel exhibiting excellent anticorrosion and pitting prevention property in the wet gas and exhaust condensate produced in the muffler and associated pipes (hereinafter collectively referred to simply as the muffler) for emission of the exhaust gas produced in the engines of automobiles, motorcycles and the like.
2. Description of the Prior Art
In automobiles, motorcycles and the like, the high-temperature exhaust gas produced in the engine passes through an exhaust manifold, a catalytic converter, etc., a center pipe, a muffler and a tail pipe to the exterior of the exhaust system. As the temperature of the muffler is low at the time the engine is started, moisture contained in the exhaust gas condenses and the condensate adheres to the inner wall and pools on the floor of the muffler. Since this condensate contains the CO.sub.3.sup.--, NH.sub.4.sup.+, SO.sub.4.sup.-- and NO.sub.3.sup.- components of the exhaust gas as well as Cl.sup.- and small amounts of organic substances, it has an adverse effect on the corrosion resistance of the muffler. During engine operation, since the temperature of the muffler rises with increasing temperature of the exhaust gas, the ammonia and the like contained in the condensate vaporize, causing the pH of the condensate to change from alkaline to acidic. For producing mufflers appropriate for such an environment, the practice has been to use Al-coated steel sheet or steel sheet containing Cr.
However, since the increasing severity of exhaust emission regulations in recent years has led to diversification in muffler use conditions, mufflers fabricated of the aforesaid steel sheet materials are no longer able to provide adequate corrosion resistance and consequently have relatively short service lives. A demand has thus arisen for corrosion resistant materials capable of increasing automobile safety while also extending muffler service life. In response to this demand, Japanese Patent Public Disclosures No. 63(1988)-143240 and 63(1988)-143241 propose steels containing 5 to 10% Cr, but even such steels are unable to meet recent needs for extended service life.